Transport networks serve for the physical layer transport of tributary signals. Such tributaries are multiplexed together according to multiplexing rules to form higher bitrate multiplex signals for a more efficient transport through the network. A well known type of transmission networks conforms with the SDH standard ITU-T G.707, 10/2000, which is incorporated by reference herein. The US equivalent of SDH is referred to as SONET.
In SDH, tributary signals are mapped into virtual containers of appropriate size. Lower order virtual containers are multiplexed into higher order virtual containers. The higher order virtual containers are mapped into frames where they are addressed by a higher order pointer called the administrative unit (AU) pointer, which allows them to float freely inside the frames so as to balance phase and frequency deviations in the network. Similarly, the lower order virtual containers are addressed inside the higher order virtual containers by lower order pointers called the tributary unit (TU) pointers.
The basic frame structure is called STM-1 (synchronous transport module). Higher capacity signals are obtained by bytewise multiplexing N STM-1 signals to form an STM-N signal.
Virtual connections, which are referred to as paths, are established within the network through the use of network elements that are capable of switching these virtual containers from any to any I/O port in space and time domain. This process is typically referred to as crossconnecting because such virtual connections are of semi-permanent nature. Such network elements are therefore also termed crossconnects.
For an SDH network, there exist basically two types of crossconnects, namely broadband crossconnects that are capable of switching higher order virtual containers, only, and wideband crossconnects that are capable of switching both, higher order and lower order virtual containers.
The core of a crossconnect is its switching matrix. Depending on the required matrix capacity, some crossconnects use a square switching matrix, while others have a multi-stage switching matrix such as a Clos matrix. Wideband crossconnects have often a higher order switching matrix and a separate lower order switching matrix. A generalized logical block diagram of such an architecture is shown for example in ITU-T G.782 01/94, FIG. 3-9.
In the existing networks, a need for more and more switching capacity arises as the traffic volume increases, particularly in metropolitan area networks. On the other hand, network operators request more compact and cost-effective network elements that require less footprint space while providing at the same time lower power consumption and reduced heat dissipation. It is therefore an object of the present invention to provide a compact high capacity wideband crossconnect.